University of Minnesota
School of Physics & Astronomy

Spotlight

Wygant heads storm belt probe research team

John Wygant
John Wygant
Wendy Tschampl
                                                       

School of Physics and Astronomy Professor John Wygant has been made Principal Investigator of a large NASA investigation to measure intense electric fields in the Earth's radiation belts. This project is part of a two spacecraft mission called the Radiation Belt Storm Probes, which will study energetic charged particle acceleration in the Earth's magnetosphere during major geomagnetic storms.

The inner magnetosphere is a region of charged, energetic particles or plasma that is trapped by the Earth’s magnetic field. Although the radiation belts are close to home and were discovered in the late 1950s during the launch of the first American spacecraft, the mechanisms responsible for creating the belts and destroying them are not known because the radiation is so intense that is it is hazardous to spacecraft. The project could have long term effects, not only for studying our own planet, but others in our solar system such as Saturn and Jupiter which also have substantial radiation belts.

Professor Wygant leads the Electric Field and Waves (EFW) team that will design and build the instrument. The electronics will need to have special shielding to protect it from radiation and a program of careful testing before the mission is launched 2012. The main instrument will measure low frequency electric field wave variations ranging from milliseconds to hours and over spatial scales of 1-100,000 kilometers. These electric fields are measured using three pairs of sensors. Two pairs of sensors are deployed at the ends of 50 m booms, that are held in place by the tension associated with centripetal acceleration of the spinning spacecraft which rotates every 10 seconds.

Wygant’s group is interested in the physics of the particle acceleration in the radiation belt, where particles maybe accelerated from low energies (1 keV) to relativistic energies (15 MeV) in a short amount of time. Wygant says that though it was previously believed that the acceleration took days to months to occur, recent data has shown that particles can be accelerated in milliseconds to hours through a variety of different mechanisms. Some of these mechanisms include large scale shock waves launched from the sun, episodes of explosive release of magnetic energy stored in the magnetosphere of the earth, electric fields associated with magnetic fields lines that can vibrate like violin strings, and a menagerie of small scale waves which propagate along magnetic field lines. “Particles find a wave to surf on, they pick up speed, and accelerate to relativistic energies,” Wygant explains. Most of these accelerations occur either during major geomagnetic storms (which also produce intense aurora) or during encounters with high speed solar wind streams emanating from the sun. Other instruments on the spacecraft will measure the energetic electrons and ions, and the variations in the Earth's magnetic field.

Wygant says that physicists have made great strides recently in learning how to sample waves intelligently. In such a complex system it is important to get a number of small samples at the most intense part of a storm event, typically a four hour period. That is why the mission will be one with dual spacecraft that pass in and out of the radiation belt at four hour intervals. Wygant is confident that they will get samples of magnetosphere storms during the mission.

The RBSP EFW collaboration includes physicists from Minnesota, U.C. Berkeley, University of Colorado, University of Alberta, the Air Force Research Laboratory and theorists from Dartmouth.